Knowing about something and considering it fair and acceptable are two different things.
A logical argument would be: "they knew about working well below market so they shouldn't act surprised" (because knowing in advance and acting surprised are contradictory).
But being hurt and complaining? There's no logical contradiction between doing that and having prior knowledge that a choice would end bad for you.
(Besides they also know that for some authors that's not the case, and they could -- even legitimately for some -- think that they are better than them, and deserve the same money).
Also what's considered "market rate" and what's in 2016 a living wage have relatively little in common. Seven cents a word is the minimum 'professional' rate for short fiction, which very few people in 2016 can actually live solely on.
Or market rate of a field being the mean rate for workers of that occupation.
If it's work below market or gut chickens for a living people will tend to accept less than they feel they're worth.
But that's not the case, the market for the output of authors cannot sustain living wages, there is no 'market wage' to make. If you look closely at this and other creative professions, that has always been the case; there is always more people that want to make a living with creative work than there are people that want to pay well enough for that work so that the creators can live.
This is structural and unlikely to change barring something like basic income. The usual answer given to aspiring creator is both to generate the income you need to live in the service industry, say as a waiter, and also to be your own agent and pimp out your professional services yourself.
